In Magnetic Resonance Imaging (MRI), three gradient amplifiers and three associated magnetic field gradient coils are typically used to provide 3-dimensional spatial encoding of atomic spins located in a magnetic field.
These gradient amplifiers are typically characterized by high peak power (several 100 kW up to 2 MW for present-day specimens) and high precision of the generated current waveforms. Circuits consisting of series-connected full bridges using pulse-width modulation (PWM) have been used to construct gradient amplifiers.
This circuit topology is known under several names, such as “stacked H-bridges”, “cascaded H-bridges”, or “cascaded multicell converter”. A severe disadvantage of the circuit is that every bridge needs an individual, floating power supply that is well-isolated against both low frequencies and high frequencies. Variations on this basic theme are possible, but at the cost of increased complexity and maintaining the need for multiple isolated power sources.
U.S. Pat. No. 7,116,166 B2 discloses the use of full bridge circuits for the construction of a gradient power supply for magnetic resonance imaging equipment.